1. Field of the Invention
The present invention relates to fluid devices and particularly to those of the variable displacement axial piston type which may function either as a fluid pump or as a fluid motor.
2. Description of the Prior Art
Heretofore, fluid pumping or motoring devices of the axial piston type have been constructed of a metallic housing having a revolving cylinder barrel with a plurality of parallel cylinder bores therein, within which pistons are reciprocated by means of a thrust plate assembly or the like. A rotary valve mechanism in the form of cylinder ports at one end of the cylinder barrel alternately connects each cylinder bore with an inlet and an outlet passage of the device as the cylinder barrel is rotated.
The thrust plate assembly in fluid devices of the variable displacement type normally takes the form of a yoke having transversely extending pintles rotatably carried in bearings suitably mounted to the wall of the housing. Suitable means are provided to pivot the thrust plate with respect to the longitudinal axis of the drive shaft on which the cylinder barrel is rotated so as to vary the amount of reciprocal stroking movement imparted to the pistons within the cylinder bores and thereby permit a selected variation in the fluid displaced by the axial piston fluid devices.
In such previously constructed axial piston fluid devices, the displacement control mechanism used to control the inclination of the thrust plate assembly with respect to the longitudinal axis of the drive shaft has necessitated a different design for the fixed displacement device and the variable displacement pump as the displacement control mechanism is normally constructed as an integral part of the housing in variable displacement devices, and thus a variable displacement device requires a larger housing than a fixed displacement device. Heretofore, the same housing could not be used for both variable and fixed displacement devices, as a larger housing is required for the variable displacement device since a portion of the housing is needed to mount the displacement control mechanism. The use of a variable displacement housing in a fixed displacement device results in an unduly large unit in proportion to its displacement. It would therefore be desirable to provide a housing having a construction adapted to accommodate both variable displacement and fixed displacement devices without requiring a larger housing for the variable displacement design.
It has also been a conventional practice to construct such previously used devices with only one type of displacement control mechanism, that is, a different application requiring a different type of displacement control mechanism, such as a manual control or a pressure compensated control, would require a major disassembly of the device to convert from one type displacement control mechanism to another or would require a different housing construction for each type of displacement control mechanism. It would therefore be desirable to provide a construction which permits an easy interchangeable use of different types of displacement control mechanisms.